Fuel tanks on board vehicles of various kinds generally have to meet sealing and permeability standards in relation to the type of use for which they are designed and the environmental requirements that they have to satisfy. At the present time, both in Europe and throughout the world, there is a substantial tightening of the requirements regarding the limitation of pollutant emissions into the atmosphere and into the environment in general.
To limit these emissions, care is taken in particular to position the accessories (ventilation lines, valves, baffles, stiffeners, etc.) inside the tank and/or the fill pipe (see in particular Application WO 2004/024487 in the name of the Applicant). However, when these components are fastened to the tank after it has been molded, it is generally necessary to make at least one opening in the tank so as to be able to introduce said components into the tank and to fasten them thereto. Hence there may be potential sealing problems near this opening.
Several years ago the Applicant therefore developed a process of initially molding a cut parison (cut into two sections) in order to be able to introduce thereinto and fasten thereto accessories during the actual molding of the tank and to thus avoid drilling openings (see Patent EP 1 110 697 in the name of the Applicant).
The Applicant has also developed a particular method for this fastening (in situ snap-riveting, the subject of Applications WO 2006/008308, FR 0756411 and PCT/EP2007/051326, the content of which is also incorporated by reference into the present application).
This technique, which is common in the field of metallurgy and that consists in molding a rivet in situ, from molten material that has been allowed to flow in and/or through an orifice of the part to be fastened and then that is left therein to solidify so as to form in situ a snap rivet or sort of rivet/bolt, has, however, several drawbacks.
The Applicant has specifically observed that in order for the material to be able to effectively flow into the snap-riveting orifice and optionally to overflow therefrom, it is necessary that this orifice has a diameter greater than 1 cm, even at least equal to 2 cm. A single fastening point is not generally sufficient to obtain a reliable fastening (to obtain therefrom one having a perfect isostatism, it is ideally necessary to provide 3 fastening points that unequivocally define a fastening plane for the part, thus avoiding an unsatisfactory fastening). Hence, this technique is not suitable for parts of small dimensions.
Moreover, in the case where the parts to be fastened are heavy, if it turns out in practice that the number of snap-riveting orifices is not sufficient to be able to support the weight of the part without damaging the parison or the wall of the tank, it will be necessary to profoundly modify the mold of the injection-molded part, the mold of the fuel tank and the snap-riveting tool in order to insert therein one or two supplementary snap rivets.